1. Field of the Invention
This invention relates to a method for enhancing the reliability of performance of a measurement system and rendering the measurement system tolerant of failure, and more particularly to a method for promoting the elevation of reliability of a system for the measurement of a plurality of physical quantities and warranting the tolerance of the measurement system against failure by adding to the measurement system the irreducible minimum of redundant element.
2. Description of the Prior Art
Numerous industrial systems require addition thereto, as a sub-system therefor, of a measurement system which measures the magnitudes of various physical quantities such as temperature and pressure and feeds the measured values to a computer. A diagram illustrating the concept of this measurement system is illustrated in FIG. 1.
A measurement system 3 is interposed between a process to be measured 4 and a computer 5. It is composed of a sensor unit 1 for transducing the magnitude of a physical quantity under measurement which is analogous in nature into another analogous quantity 7 such as voltage and a data acquisition system (such as, for example, an A/D converter) for feeding the measured value 8 into the computer 5.
When a great distance separates the objective process of measurement 4 and the computer 5 from each other, the data acquisition system 2 incorporates therein, as a sub-system therefor, a transmission system for transferring the sensor output.
Generally when failure develops in the measurement system 3, the operation of the system as a whole becomes abnormal. To promote the elevation of reliability of the industrial system as a whole, therefore, the measurement system 3 which is a sub-system for the industrial system is required to provide highly reliable performance.
Thus, it is essential that the measurement system 3 should be rendered tolerant of failure by some means or other, namely, it should be made to function correctly at least in outward appearance even when failure occurs in part of the measurement system 3.
To render the measurement system tolerant of failure, it is generally necessary that the "method for conferring redundancy upon the system" should be unified with the "method for repair of failure" which is capable of detecting the failure, identifying the failure, isolating the failure, and effecting recovery from the failure by processing the redundant signal issuing fron the former method.
It is the TMR (triple modular redandancy) method which has found popular recognition as a method available for rendering the measurement system tolerant of failure. For the purpose of rendering the system redundant, this method triples sensors and other component elements required for handling every physical quantity under measurement. And for the purpose of "reconfiguration of failure," this method applies the logic of decision by majority to the three measured values. In case where r physical quantities are to be measured, this method requires preparation of 3r sensors. Thus, this method triples the component elements of hardware. This method, accordingly, suffers from a disadvantage that the measurement system will have increased volume and weight and the cost of equipment will be proportionally increased.